The inventors have filed several patents concerning propulsion systems and installations thereof, using gases, especially compressed air, for completely clean operation in urban and suburban sites:
WO 96/27737—WO 97/39232—WO 97/48884—WO 98/12062—WO 98/15440—WO 98/32963—WO 99/37885—WO 01/69080—WO 03/036088
In their international patent application WO 99/37885, to the content of which reference may be made, they propose a solution which increases the amount of usable and available energy, wherein the compressed air, before being introduced into the combustion and/or expansion chamber, from the storage tank, is directly, or after having been passed through the heat exchanger or exchangers of the ambient thermal energy recovery device, and before being introduced into the combustion chamber, is conveyed to a thermal heater where, as a result of its temperature increasing, it will further increase in pressure and/or in volume before being introduced into the combustion and/or expansion chamber of the engine, thereby again considerably increasing the performance that can be achieved by the said engine.
The use of a thermal reheater, and despite the use of a fossil fuel, has the advantage of being able to use clean continuous combustions that can be catalysed or depolluted by all known means for the purpose of obtaining emissions with infinitesimal pollutants.
The use of a thermal heater, and this is true in spite of the fact that a fossil fuel is used, has the advantage that clean continuous combustion can be employed which can be catalytically converted or rid of pollution by any known means with a view to obtaining infinitesimally small levels of pollutant emissions.
The inventors have filed a patent application WO 03/036088, to the content of which it is possible to refer, relating to an additional compressed air injection motor-compressor—motor-alternator set operating on single and multiple energies.
In these types of engine operating on compressed air and comprising a compressed-air storage tank, it is necessary to expand the compressed air, which is stored at very high pressure in the tank but the pressure of which decreases as the tank empties, to a stable intermediate pressure known as the end-use pressure in a buffer capacity known as the working capacity before it can be used in the engine cylinder or cylinders. The well-known conventional regulators of the shutter and spring type have very low flow rates and using these in such an application requires very cumbersome and poorly-performing devices; what is more, they are highly sensitive to icing as a result of the humidity in the air that is cooled during the expansion.
In order to solve this problem, the inventors have also filed an international patent application WO-A1-031089764, to the content of which reference may be made, concerning a variable flow rate dynamic regulator and a distribution system for engines supplied with an injection of compressed air, comprising a high-pressure compressed air tank and a working capacity.
The inventors have also filed a patent application WO-A1-02/070876 concerning a variable-volume expansion chamber consisting of two distinct capacities, one of which is in communication with the compressed air inlet and the other one of which is twinned with the cylinder, which capacities can be placed in communication with one another or isolated in such a way that during the exhaust cycle it is possible to charge the first one of these capacities with compressed air and then establish the pressure in the second one, immediately at the end of the exhaust while the piston is stationary at top dead centre and before it resumes its stroke, the two capacities remaining in communication and expanding together in order to perform the power stroke and that at least one of the two capacities is provided with means of modifying its volume so as to allow the resultant engine torque to be varied at the same pressure.
In the operation of these “charge expansion” engines, the filling of the expansion chamber always represents an expansion without work prejudicial to the overall efficiency of the machine.
In order to solve the abovementioned problem, the inventors have also filed a patent application WO-A1-2005/049968 describing an engine with an active chamber in which the expansion chamber consists of a variable volume equipped with means for producing work and is twinned and in permanent contact via a passage with the space above the main driving piston.
WO-A1-2005/049968 (FR-A1-2.862.349) in particular illustrates a four-phase thermodynamic cycle in operation in compressed air mono(single)-energy mode, characterized by:                an isothermal expansion without work;        a transfer-slight expansion with work said to be quasi-isothermal;        a polytropic expansion with work;        an exhaust at ambient pressure.        
The engine operates on the above thermodynamic cycle and uses a conventional connecting rod/crank arrangement. It is preferably supplied with compressed air or any other compressed gas contained in a high-pressure storage tank through a buffer capacity known as the working capacity. The working capacity in the dual-energy version comprises a device for heating the air which is supplied by an additional energy (fossil or some other energy source) so as to increase the temperature and/or the pressure of the air passing through it.
In this latter document WO-A1-2005/049968 (FR-A1-2.862.349), such an operation an thermodynamic cycle are obtained by mechanical means connecting the main drive piston, the working crankshaft and the piston of the active expansion chamber.
It is an object of the present invention to simplify the design of such an engine, while keeping all the above mentioned advantages.